Libyans face extraordinary uncertainty as the Ramadan holiday gets under way, though Muammar Gaddafi's boastful claim that the tide of war is turning against his rebel enemies and their Nato supporters looks wildly premature.

"The will of the Libyan people is stronger than Crusader aggression," the "brother leader of the revolution" declared in his latest characteristically defiant address, pledging "never to abandon" the battle.

Gaddafi was quick to gloat about the mysterious assassination of Abdel Fatah Younis, his former interior minister who defected to become military commander of the Benghazi-based opposition. To Gaddafi it proved the movement is disorganised and incapable of running the country, just as, to his evident fury, it had won wide international – and then British – recognition as the legitimate government of Libya.

Tripoli has tried unsuccessfully from the beginning of the crisis to portray the rebels – who certainly include significant Islamist elements – as promoting an al-Qaida agenda, so ostensible evidence of internecine strife is useful for propaganda reasons. Yet it remains possible the "rogue" action that killed Younis may have been carried out by a "fifth column" working for the Gaddafi regime – no slouch when it comes to deception and clandestine operations. That explanation is, naturally enough, the one favoured by the National Transitional Council which is investigating the incident.

"Regrettable but containable," is the official council line about his death.

"This is not a revolution based on one man," one opposition official said. "It is based on six million people." Another avenue of speculation is that Younis might have been playing a double game.

News of fighting involving rival Islamist factions came as yet another worrying sign of internal division at a time when western political and military support for the rebels has reached the point of no return.

The bigger question is whether the disarray in Benghazi, compounded by new reports of dissent in the coastal enclave of Misrata, will slow an accelerating though still uneven military momentum, backed by Nato air power, with rebel forces in the western mountain areas now getting uncomfortably close to Tripoli.

Mustafa Abdel-Jalil, the NTC chairman, clearly understood the need for calm and continuity when he announced the appointment of General Suleiman Mahmoud al-Obeidi – by no coincidence a member of the same powerful eastern tribe as Younis – as interim chief of staff.

Younis's killing has deepened concern among the rebels' western and Arab backers, who are worried about a lack of unity and the Islamist influence. But the rebels are, at the end of the day, the only anti-Gaddafi forces available.

"These events are embarrassing but I don't think they will affect the overall thrust of Libyan events," said Ashour Shamis, a London-based opposition activist and commentator.

The US, Britain, France and Nato as a whole have invested far too much to abandon this war in the face of one setback, however serious. The bombing of Libyan state TV satellite transmitters in Tripoli suggests the overall alliance strategy is continuing. France, hawkish from the start, vowed to carry on, with its defence minister Gerard Longuet calling for an uprising in Tripoli. It looks like being a long hot Ramadan in Libya.